Purple Landings

Published: Autumn 2005

In the not distant future you may notice two remarkable things about a landing airplane: The landing gear glow purple and the landing is much quieter than you’d expect. The two linked curiosities result from some innovative technology developed at Notre Dame.

For some time, engineers have known they could make an airplane touchdown less noisy by streamlining the landing gear. Manufacturers, however, haven’t incorporated the designs because mechanical wind screens add weight, don’t stow easily and are difficult to maintain.

Now, however, Flint O. Thomas and Thomas Corke, Notre Dame professors of aerospace and mechanical engineering, have come up with a novel, nonmechanical way to streamline landing gear by ionizing the air around the apparatus. The concept is elegant: Strategically placed electrodes linked by a dielectric material, which supports electrostatic fields, produce a glowing purple plasma of ionized air that sucks surrounding air down, channeling it near the surface. Since noise is created when air flow separates from a surface, the streamlining effect of the plasma significantly reduces airplane noise by keeping the flow close to the landing gear.

In wind tunnel tests at Notre Dame, Thomas and Corke have demonstrated that just two plasma actuators reduced aerodynamic drag by 90 percent and significantly suppress noise. “With refinements we’re confident we can do even better than that,” Thomas says.

The plasma streamliners have several advantages, the Notre Dame researcher says: They don’t require a great deal of power, can be turned on as needed, are relatively inexpensive and can easily be retrofitted to existing aircraft. The commercial airplane industry is keenly interested in the technology.